I was thinking the exact same thing. Would not surprise me in the least if “concerned parties” in Iran let the US know exactly when Soleimani would be landing.
It would be a good way to eliminate a powerful military leader without risking the military deposing the clergy.
Based on several media reports, it seems we've been keeping a pretty close eye on him and monitoring his travels. We seem to know his itinerary over the past few weeks leading up to his landing in Baghdad. I'm guessing our intelligence folks are still hard at work and this is a successful operation for them.